There are two kinds of buses that run through the city. One is the metro-bus, which is linked to the metro system, and takes passengers where the tube does not go. The second is the privately owned Carritos.
Privately owned carritos, a bit less expensive and much quicker than the metro-buses, service a larger part of the city. These are not the best kind of transport, with intolerable radio bass levels and dilapidated seats, but they will usually get you to the very doorstep of your destination. In fact, you choose where you want to get off, as there really are no existing bus stops. Just yell “Para aqui!” at the place you want to hop off, and the carrito will come to a stop! Kind of like pulling the emergency chain on a train.
The routes for each carrito are displayed on the windshield. The carrito service ceases at around 9pm.
Word of advice: watch out for pick pockets.